Cathode-ray tube



May 312, 1970 G. A. w. VERMEULEN ET AL 3,511,678

cATHoDn-RAY TUBE Original Filed Jan. 14, 1963 INVENTORS GAJY. VERMEULEN J.C. GRAVESTEYN United States Patent 3,511,678 CATHODE-RAY TUBE Gerardus Antonius Wilhelmus Vermeulen and Jacobus Cornelis Gravesteyn, Emmasingel, Eindhoven, Netherlands, assignors to U.S. Philips Corporation, New York, N.Y., a corporation of Delaware Continuation of application Ser. No. 251,406, Jan. 14,

1963. This application July 29, 1966, Ser. No. 568,976 Int. Cl. H011 29/18 U.S. Cl. 117-335 4 Claims ABSTRACT OF THE DISCLOSURE This application is a continuation of application Ser. No. 251,406, filed lan. 14, 1963, now apandoned, which was a continuation-in-part of application Ser. No. 116,166, tiled June 9, 1961, now U.S. Pat. 3,226,246.

Our invention relates to a display screen for a cathoderay tube and to a method of manufacturing the same. More particularly, the invention relates to a method of manufacturing a luminescent screen for a cathode-ray tube comprising two or more materials applied to discrete surfaces of a transparent support and luminescing in different colors upon excitation -by electrons.

In our earlier application we have described a method of manufacturing a luminescent screen for a cathode-ray tube in which, for example, two or more phosphors are applied to discrete areas of a transparent support, after which a layer of photosensitive binder is applied over the phosphors and the areas between the phosphors. The photosensitive binder is thereafter exposed through the support to radiation which hardens it in those areas where thereis no phosphor material. A filter is provided between the transparent support and the photosensitive binder covering the phosphor material so that hardening radiation transmitted through the support does not harden the photosensitive binder covering the phosphors and can be removed by dissolving and washing it away. In the areas between the previously applied phosphors, however, the binder is hardened and serves as a support for the application of another phosphor.

The present invention is an improvement in the method disclosed and claimed in said application. If no filter were provided between the transparent support and the photosensitive binder covering the phosphor material and if the phosphor material would not exhibit a filtering action with respect to the hardening radiation, the hardening radiation may also result in some hardening of the binder covering the luminescent materials previously applied.

It is an object of our invention to avoid hardening of the radiation hardenable material which is applied over luminescent materials while hardening the material covering areas of a transparent support of a cathode-ray tube prior to application of another luminescent material over those areas.

This and further objects of the invention will appear as the specification progresses.

In accordance with out invention we expose the photosensitive binder from the side remote from the support to the inuence of hardening radiation at those areas at which the discrete surfaces of the last luminescent materials are desired and also expose it through the support to the influence of a hardening radiation in a manner such that substantially no hardening of the photosensitive binder takes place at the previously applied discrete surfaces of the other luminescent materials. Satisfactory adhesion to the carrier is thus obtained. It is unnecessary for the previously applied surfaces of the luminescent materials to be relatively impermeable to the hardening radiation through the support employed for the last luminescent material, since this radiation has only an intensity such, and is used only for a period such that substantially no hardening of the photosensitive binder takes place at the previously applied discrete surfaces of the other luminescent materials. Since the hardening radiation through the support causes the photosensitive binder to be hardened over substantially the Whole contact surface With the carrier satisfactory adherence is obtained. Although, in view of the properties of the previously applied discrete surfaces of the other luminescent materials, a smaller amount of radiation may be used for the radiation through the support, it has surprisingly been found that the last luminescent material still distinctly adheres to the whole surface area of the support which is not yet covered, which adhesion is furthermore such that for the radiation from the side remote from the support at the discrete surfaces of the last luminescent material an amount suices which is considerably smaller than that which is necessary if radiation takes place only from the side remote from the support. The duration of the radiation from the side remote from the support may thus be shortened.

lf, in addition, the photosensitive binder is exposed to the influence of the hardening radiation at the same time from the side remote from the support and through the support, a gain in time in the manufacture is also realized.

The other luminescent materials may have been previously applied in discrete surfaces in various Ways. This may have been effected by suspending the luminescent material in a solution of a photosensitive binder, spreading the suspension on the support, followed by drying, and then directing hardening radiation onto those areas at which the discrete surfaces of the luminescent material are desired. The binder then becomes locally insoluble in the solvent. The luminescent material can be removed from the unexposed areas by washing with the solvent.

Also a solution of the photosensitive binder which does not contain luminescent material may be spread on the support and exposed at given areas. The binder becomes insoluble at the exposed areas, but remains a little sticky, at least if the exposure has not lasted too long. A suspension of the luminescent material to be applied is then spread in a suitable medium over the locally exposed layer of binder to which the grains of luminescent material adhere, no adhesion taking place on the unexposed portions which are not sticky. The unexposed binder and the luminescent grains on it are removed completely by rinsing with the solvent for the unexposed binder.

If three materials luminescing in red, green and blue colors respectively are applied in the described manner, then preferably the red luminescing material, i.e., Zinccadmium sulphide activated with silver should be applied last, since this material is least permeable to the radiation employed in hardening the binder.

The thickness of the last luminescent layer obtained in the described manner is not uniform but depends upon whether the binder has been hardened at the particular area only through the support or both through the support and from the side remote from the support. The invention therefore also relates to a cathode-ray tube for color display having a display screen manufactured in 3 the manner described, the luminescent material applied last iilling thev whole surface area of the support of the viewing screen between the previously applied discrete surfaces of the other luminescent materials and having a layer thickness which is larger in discrete areas.

More particularly the invention relates to a cathoderay tube of the kind in which a thin reflecting metallic layer, permeable to electrons, is present on the side of the screen remote from the support, resulting in a great improvement in contrast.

The invention will be described with reference to the drawing:

FIG. 1 shows a display screen for a cathode-ray tube according to the invention.

FIG. 2 shows a cross section of the display screen of FIG. 1 along the line II-II.

FIG. 3 shows a cross section of the display screen of FIG. 1 along the line III-III.

In a specific embodiment of the method according to the invention, a glass support 1 was used for the luminescent screen on which discrete circular surfaces of two differently luminescing materials, namely, green 2 and blue 3, were present. A zinc-cadmium sulphide activated with silver was used for green and a zinc-sulphide activated with silver was used for blue. A suspension of red-luminescing zinc-cadmium sulphide activated with silver in an aqueous solution of polyvinyl alcohol containing a bichromate as a sensitizer was spread over the glass support and the surface of green and blue-luminescing materials forming a layer 4 which was irradiated at discrete circular areas for minutes by means of a mask from the side remote from the support by a `900-watt lamp which produced inter alia radiation in the light region of the polyvinyl alcoholbichromate system, that is to say from 3,650 to 4,380 angstrom. The layer was also evenly irradiated for 15 seconds through the support by four 12S-watt lamps producing the same radiation. Portions of the solvent were made insoluble by these radiations. Subsequently, the unexposed binder With the luminescent material contained in it was removed by means of water. This resulted in a red-luminescing layer 4 satisfactorily adhering to the support by means of a hardened photosensitive binder,`

which layer fills the whole surface area of the carrier between the discrete blueand green-luminescing surfaces andwhich has a thickness which was greater at the portions irradiated through the mask.

While we have described our invention with reference to a specific embodiment thereof, other modifications will be apparent to thoser skilled in the .art without departing from the spirit and scope of the invention as defined in the appended claims.

What we claim is:

1. A method of manufacturing a display screen for a cathode ray tube comprising the steps of, depositing on a transparent support having a first luminescent material covering selected areas thereof a photosensitive binder, exposing the photosensitive binder through the support to hardening radiation having only an intensity at which substantially no hardening of the photosensitive binder occurs at the areas previously covered with the luminescent material, exposing the binder from the side remote from the support at those areas at which another luminescent material is to be deposited for a limited time to harden the same only at those areas between the areas previously covered with the luminescent material, and Washing the thus coated screen to remove the photosensitive binder covering the irst luminescent material.

2. A method of manufacturing a display screen for a cathode-ray tube as claimed in claim 1 in which the photosensitive binder is mixed with a luminescent material emitting light of different spectral distribution than that of said luminescent material which covers selected areas when said luminescentmaterials are struck by electrons.

3. A method as claimed in claim 2 in which the photosensitive binder mixed with the luminescent material is applied over two luminescent materials covering discrete areas each of which emit light of different spectral distribution when said luminescent materials are struck by electrons.

4. A method as claimed in claim 3 in which the luminescent material mixed with a binder is zinc-cadmium sulfide activated with silver.

References Cited UNITED STATES PATENTS 3,005,708 10/1961 Hesse 96-36.1 2,873,189. 2/1959 Evans et al 9635 3,025,161 3/ 1962 Rychlewski 96-35 3,224,895 12/1965 Rebel 117-335 XR 3,226,246 12/ 1965 Vermeulen et al. 117-335 XR ALFRED L. LEAVITT, Primary Examiner W. F. CYRON, Assistant Examiner 

